1. Field of the Invention
This invention relates generally to internal combustion engines, and more particularly plastic covers for internal combustion engine applications.
2. Related Art
Covers for internal combustion engine applications, such as valve covers and rear engine covers for automotive and other internal combustion engine applications typically are made of die cast metal, metal stampings or molded thick-walled thermoset or thermoplastics materials. The covers typically have an elongated trough-like structure and have a perimeter flange formed with a series of spaced bolt holes that enable the cover to be bolted onto an associated cylinder head or rear portion of the engine. Use of the above materials (including the thick-walled plastics materials) is due in large part to the requirement that the cover have sufficient structural stiffness and stability under changing operational conditions (e.g., temperature, vibration, loading) to support and maintain a good seal with a seal gasket that is typically placed between the valve cover and the cylinder head to avoid oil leakage between the cover and head.
The all-metal valve covers are common, but are costly and heavy. The thick-walled all-plastic valve covers can be less costly and can contribute to a reduction in weight, but often the structural and dimensional stability requirements call for such large wall thicknesses that the benefits offered by the plastics material are offset by the bulkiness of the product and space requirements taken up by the added wall thickness. The thermoset materials are relatively stiffer than the thermoplastics materials, but they are more costly. Another issue with all-plastic covers is the need for added fasteners as compared to the all-metal covers in order to adequately prevent leakage. As such, the span between adjacent bolt holes is decreased and the number of fasteners is increased compared to metal valve covers, thus, adding to the cost and weight of the valve cover assembly. To date, a commercially suitable plastic valve cover that takes advantage of the benefits of what plastics have to offer has not been fully exploited, due in large part to the structural and dimensional limitations of the available plastics materials.